The invention relates to optical apparatus for uniformizing light from a light source and delivering the light to a light valve. In particular, the inventive apparatus makes use of an optical system, including a light transmitting tunnel, to receive non-homogeneous light from an extended light source and deliver uniform illumination onto a light valve.
Recently, considerable interest has arisen in applying liquid crystal display technology as well as the technology of deformable mirror devices to implementation of projection systems. Such applications usually require a uniform illumination of the light valve, viz., the liquid crystal display or the deformable mirror device, in order to provide a uniform, stable projection image. In most applications, the projection system design specification includes space limitations, viz., the distance between the light source and the light valve. The light valve and its illumination system must fit into a restricted space. For light valves which are sensitive to infrared or ultraviolet light, such as the liquid crystal or deformable mirror device, the space restriction leads to a requirement for efficient removal of these wavelengths from the light beam.
Thus, a need exists for a compact light valve illumination system which provides for uniformity of light across the active area of the valve. Furthermore, there is a need for a light valve illumination system which makes efficient use of light power and which provides a means for directing infrared and ultraviolet light away from the valve. In addition, low cost and light weight are required for the projection system to be commercially competitive.
A light transmitting tunnel is described in U.S. Pat. No. 3,170,980, Pritchard. However, in this patent the tunnel specifications are rigorous to an extent that the tunnel could not readily be incorporated into a light valve illumination system. ". . . manufacturers of high precision optical equipment state that the glass used in making the optical tunnel should have no dimension ratios greater than roughly 5:1." (Col.2, II. 19-22) "This limitation means that the weight of the optical tunnel increases enormously as its length increases." (Col.2, II. 26-28).
In U.S. Pat. No. 5,059,013, Jain, there is a system described relating to, ". . . method and apparatus for providing a light beam of selected cross section shape and uniform intensity, and which emits self luminously into a selected numerical aperture." (Col. 1, II. 11-14) However, the system is complicated and expensive in that it makes use of a polygon aperture, a light expanding and trimming sub-system, a laser, a second light source and a number of other components as set forth in the method section. (Col. 4, I. 48 to Col. 5, I. 32.)